The Theory of Rhythm in Music

So far we’ve said little about a vital aspect of all music—the rhythm, beat or sense of groove. Listen to any iconic pop or rock tune, and it is that particular combination of melody and rhythm combined that makes it recognizable for what it is.

Famous pop ‘hooks’ that have stuck in our minds exist in abundance and often do so because they are quirky, or push the boundaries in some way, or even blatantly break the rules of music - which are of course made to be broken like any rules! But it does help if we know what the rules are in the first place, so with that in mind let’s try to cover the basics quickly.

“Everything in the universe has a rhythm, everything dances” – Maya Angelou

Notes and Rests

Notes and rests (musical silences) can obviously be of different lengths, and are written according to the following chart. As represented below, each note or rest to the right lasts half as long as the one to its left, so a half note or minim lasts half as long as a whole note or semibreve.

Not everyone follows the North American naming system, so I’ve also included below the names commonly used in places like the UK. So choose whichever you’re most familiar with.

In addition, notes can be dotted. The dot adds half the value of the note to itself:

Rests can occur at the beginning of a musical phrase or at the end. In a song, they also often occur between the different phrases of the melody, allowing the singer to breathe. (This also applies for most orchestral instrument melodic phrasing.)

In music notation, there are various conventions that govern how these are usually written so as to make up correctly mathematical bar lengths and phrases. But this is really outside the scope of this article, and are what young music students routinely have to master in order to pass theory exams!

Time Signatures: Beats in a Bar

At the beginning of any piece of sheet music will be the time signature, which tells you what meter the piece is played in. Time signatures consist of two numbers. The top number tells you how many beats there are in each bar. The bottom number tells you what kind of beat we are talking about. So, the number of beats and the value of each beat.

For example, 4/4 tells you there are 4 beats of quarter notes or crotchets in each bar. 6/8 tells you there are six beats of eighth notes or quavers. Time signatures that have either 2,3 or 4 beats to a bar are usually called simple time. Time signatures like 6/8, 6/4, or 9/8 are called compound time. Other less common time signatures also exist, such as 7/8 or 5/4 (famously in Dave Brubeck’s jazz piece ‘Take Five’).

The time signature tells you that throughout that piece there will be a flow of strong and weak beats that normally follow this same pattern in each bar, unless interrupted by accents in unexpected places. Here’s four of the most common time signatures and how strong and weak beats would normally follow each other:

Since I touched on the subject of unusual time signatures, let’s take a moment to listen to Dave Brubeck’s ‘Take Five’, which is written in 5/4 time... or is it? Some have said it is really a succession of alternating 3/4 and 2/4 bars if you listen to where the strong and weak beats fall in the piano accompaniment, in relation to the melody. You be the judge!

Beats and Pulse: What's the Difference?

Both bars and beats can have any number of notes in them, so beats are not synonymous with actual notes. In the above time signature examples, I’ve subdivided the beats into eighth notes or quavers to demonstrate this point. The stress marks indicate where the actual beats fall.

So a bar of 3/4 time has three beats in each bar. You can see from this that simple time signatures tend to have beats that naturally divide in two, whereas beats in a compound time signature like 6/8 divide into three. It follows from this that the underlying pulse of any piece of music might be exactly equal to the number of beats, or it might be a subdivision of each beat like the eighth notes in the example above.

Let’s listen to a couple of rock music examples with different time signatures that illustrate exactly this point; the difference between beat and pulse.

Here, the time signature is clearly 4/4, but the underlying pulse is evidently the steady eighth note rhythm of the guitar. The melody actually starts before Beat 1, and the strong first beat of the bar falls on the word ‘take’ at the beginning. (A melody that begins before the first beat of a bar is often called a ‘pickup’ or ‘anacrusis’.)

This is an example of 6/8 time, so (ignoring the brief introduction) the groove rolls along with a feeling of six eighth notes to a bar, whereas the chorus melody sticks to the beat quite closely, each note seems to be a dotted quarter note. So once again, pulse and beat equate to different things. The backing rhythm rolls along in a steady eighth note pulse, whereas the melody sticks to the ‘two in a bar’ beat of a typical 6/8 time signature.

Tempo

Simply the speed or pace of any piece of music, this is usually defined as a measure of the number of beats per minute in most sequencing packages. However, there are also common Italian terms used for this purpose in classical music. These are terms that tend to associate a mood with a certain speed, so they do a bit more than just tell you the speed at which to play.

The speed of the music can change during performance, of course. It can speed up, or broaden out towards the end.

It’s worth noting that the speed of your song can often be critical to its success. Too slow, and it drags. Too fast, and the singer can’t find the space to really get the lyrics across satisfactorily.

It would be nice to think that speed is purely a function of mathematics. However, any performer will tell you it is really an art rather than a science. They will vary their performance speeds in subtle ways according to the mood of their audiences, or the context of the performance occasion.

Syncopation & Cross-rhythm

Technically, a syncopation is a displaced beat, where the accent occurs in an unexpected place; i.e. a strong beat where one would have expected a weak one. Whole music genres have been built around employing certain types of syncopation as a part of the language of the music.

In reggae, the strongest beat in the bar tends to be on the third beat of a 4/4 bar rather than the first. So the drummer would play to that, and maybe ‘fill’ differently to how he might if playing a rock song. The guitarist also typically emphasizes the off beats in each bar.

Jazz, especially modern jazz, takes the art of syncopation to an extreme degree of complexity. It’s how we recognize it for what it is.

Whether it is the strong ‘fours to the floor’ of a club track, or a gliding waltz or minuet in 3/4 or 6/8, dance music tends to rhythmic regularity. But there are plenty of examples of music in other cultures around the world that employ complex cross-rhythms, or focus on strong syncopation.

In any situation where groups of musicians play together and combine different rhythms, this is called counterpoint. The rhythmic flow of a song melody sung over the drive of a backing track is an example of this, as is the playing of a orchestra.

A cross-rhythm occurs when a rhythm with a certain pulse combines with another rhythm of a different pulse; again, certain styles of ethnic dance music are defined stylistically by how this happens.